Alkali metal borate masking in galvanizing process



ay 4, 1965 N. E. COOK ETAL ALKALI METAL BORATE MASKING IN GALVANIZING PROCESS Filed Nov. 8. 1960 INVENTORS MW m mm m EL NS w United States Patent 3,181,963 ALKALE METAL BQRATE MASKlNG 1N GALVANIZENG PRUCESS Nelson E. Cook and Samuel L. Norteman, Wheeling,

W. Va, assignors to Wheeling Steel tiorporation,

Wheeling, W. Va, a corporation of Delawru-e Filed Nov. 8, 1960, Ser. No. 67,946 5 Claims. (6!. 1l7--5.5)

This invention relates to galvanizing a portion only of a ferrous metal article. It relates more particularly to the discovery of an improved masking substance for masking the portion of the article which is not to be galvanized and improved techniques in the galvanizing of articles in which only a portion of the article is to be galvanized. More specifically the invention is conconcerned with a method of galvanizing one side only of ferrous metal strip.

For purposes of explanation and illustration we shall describe the invention as practiced in the galvanizing of one side only of ferrous metal strip although it is to be understood that in certain of its aspects, particularly in respect to the employment of our improved masking substance, the invention may be otherwise practiced, as, for example, in the hot dip galvanizing of metalware.

Those skilled in the art have heretofore directed their efforts to the galvanizing of one side only of ferrous metal strip. The utility and advantages of ferrous metal strip galvanized on one side only are well understood and hence need not here be repeated. One example of a process for galvanizing one side only of ferrous metal strip which has heretofore been proposed is that disclosed in United States Patent No. 2,894,850. According to the disclosure of that patent an alkali metal aluminate solution is utilized as a masking substance to mask one side of the strip and after application of the alkali metal aluminate solution the strip is passed through a bath of molten spelter to galvanize the side of the strip which is not coated with the akali metal aluminate solution while the side coated with the alkali metal aluminate solution remains ungalvanized. The use of alkali metal aluminate solution as a masking substance is confined to a process in which the strip after application of the alkali metal aluminate solution is subjected to temperature of at least 1250 F. in a reducing atmosphere because the alkali metal aluminate solution oxidizes the strip and the high temperature heat treatment in a reducing atmosphere is required to reduce the oxide. We have tried out an alkali metal aluminate solution in a galvanizing line as disclosed in United States Patents Nos. 2,823,641, 2,824,020 and 2,824,021 in which there is no high temperature heat treatment in a reducing atmosphere and we have found that heavy oxidation persists throughout the coating process which renders the alkali metal aluminate solution useless in such a process. We have also tried out many other prospective masking substances which have proved unsatisfactory in our process. Sodium carbonate, sodium benzoate, potassium fluoride, chromic acid, magnesium sulfate, manganese chloride, potassium bromide, sodium bromide and sodium chloride all produce heavy oxidation as in the case of alkali metal aluminate and specifically sodium aluminate. Sodium acetate, potassium sulfide and sodium bromide do not adequately inhibit zinc adherence. Aluminum fluoride is too dii'licultly soluble to be practical for the purpose.

We have discovered that an alkali metal borate ideally serves the purpose as a masking substance in our process in which we do not utilize a high temperature heat treatment in a reducing atmosphere. The melting point of alkali metal borate is higher than the temperature of molten spelter so that the masking substance does not Bidlfih Patented May 4, i965 melt, and it effectively protects the side of the strip to which it is applied against oxidation. It is readily soluble in water which simplifies the application of the masking substance before galvanizing and its removal after galvanizing. If in any cases complete removal of the masking substance is not accomplished by washing with water the masking substance is entirely compatable with alkaline cleaning prior to bonderizing. Also the alkali metal borate has no deleterious effect on the zinc coating where it could be deposited in the rinse water.

Any alkali metal borate will serve our purpose. Since sodium tetraborate (borax), Na B O is most abundantly available in nature it is most practical to utilize it.

We have also discovered certain improved techniques in the galvanizing of one side only of ferrous metal strip, whether the masking substance used be an alkali metal borate or other masking substance. Our improved techniques will be referred to presently.

We provide a method of applying a protective metal coating to a portion only of a ferrous metal article while maintaining the remainder thereof substantially free from oxide, obviating a high temperature oxide-removing heat treatment, comprising coating with a solution of an alkali metal borate the portion of the article. which is not to be metal coated and dipping the article in molten coating metal whereby to metal coat the portion of the article which is not coated with the alkali metal borate while the portion coated with the alkali metal borate remains uncoated with the coating metal and substantially free from oxide and limiting the temperature of the article and the bath during such treatment to a temperature below the melting point of the alkali metal borate, thereby producing an article having a portion metal-coated and the remainder substantially free from oxide. We preferably coat with a flux the portion of the article which is to be metal-coated. We use galvanizing as an example. We coat with an alkali metal borate the portion of the article which is not to be galvanized and dip the article in molten spelter whereby to galvanize the portion of the article which is coated with flux while the portion coated with the masking substance remains ungalvanized.

More specifically we provide a method of galvanizing one side only of ferrous metal strip comprising coating one side of the strip with an alkali metal borate and passing the strip through a bath of molten spelter whereby to galvanize the side of the strip which is not coated with the alkali metal borate while the side coated with alkali metal borate remains ungalvanized. We preferably coat one side of the strip with a flux and coat the other side of the strip with a masking substance, prefably an alkali metal borate, and pass the strip through a bath of molten spelter whereby to galvanize the side of the strip which is coated with flux while the side coated with the masking substance remains ungalvanized.

We still further provide a method of galvanizing one side only of ferrous metal strip comprising passing the strip first with one of its flat sides or faces facing downwardly and then with the other of its flat sides or faces facing downwardly, applying a masking substance, preferably an alkali metal borate, to the under side of the strip on one of said passes, applying flux to the under side of the strip in the other of said passes and passing the strip through a bath of molten spelter whereby to galvanize the side of the strip which is coated with flux While the side coated with the masking substance remains ungalvanized.

We preferably apply the masking substance to the under side of the strip while the strip is passing with one of its flat sides or faces facing downwardly by use of a roller and by the applying roller deflect the strip out of a straight pass line so that the applying roller presses a 2' tightly against the strip and engages the strip by surface as distinguished from line contact.

When applying flux to one side of the strip and masking substance to the other side we preferably dry the first applied coating before the second is applied. We find it desirable to apply the flux before applying the masking substance.

Finally we provide a method of galvanizing one side only of ferrous metal strip comprising coating one side of the strip with a masking substance, passing the strip through a bath of molten spelter whereby to galvanize the side of the strip which is not coated with the masking substance while the side coated with masking substance remains ungalvanized and after the strip galvanized on one side emerges from the bath of molten spelter removing the masking substance from the strip, preferably by brushing.

Other details, objects and advantages of the invention will become apparent as the following description of a present preferred method of practicing the same proceeds.

In the accompanying drawing we have illustrated diagrammatically one form of apparatus which may be employed in practicing the invention and have shown a present prefer-red method of practicing the invention.

Referring now more particularly to the drawing, a ferrous metal strip is designated by the chain line S. The strip may come from a coil of steel strip and it may be drawn ttnough the illustrated apparatus in the direction of the arrows and subsequently either recoiled or sheared into sheets. The strip is guided by pulleys or rolls designated respectively and successively by reference numerals 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10. Before the strip reaches the guide roll 1 it is suitably cleaned to free it from oil or other undesirable materials clinging to the surface of the strip after which, between guide rolls 1 and 2, it is heated by a heating unit 11 to insure that the strip is dry and to somewhat elevate its temperature. Between the guide rolls 2 and 3 the strip, while advancing with one of its fiat sides or faces facing downwardly, is engaged by a coating applying roller 12 which deflects the strip out of a straight pass line so that the applying roller presses tightly against the strip and engages the strip by surface as distinguished from line contact. The roller 12 is journaled to rotate with its lower portion immersed in a bath 13 of flux which may be any conventional flux used in the Cook-Norteman galvanizing process, as, for example, a solution of zinc ammonium chloride. The flux is applied evenly to cover the entire under surface of the strip, the deflecting of the strip out "of a straight pass line by the applying roller insuring effective flux application throughout the entire area of the under side of the strip.

After application of the flux by the roller 12 the strip is heated by a heating unit 14 to dry the flux. Desirably the flux should be completely dry when the strip reaches the masking substance applying roller presently to be described.

The strip passes about guide rolls 3 and 4 which reverse its direction so that it moves back from left to right whereas between guide rolls 2 and 3 it was moving from right to left viewing the drawing; also the strip is inverted so that the side which was facing upwardly between the guide rolls 2 and 3 faces downwardly between the guide rolls 4 and 5. As the strip moves between the guide rolls 4 and 5 the fiuxed surface is the upper surface.

Between the guide rolls 4 and 5 the strip is engaged by a masking substance applying roller 14a analogous in structure, mounting and function to the roller 12 and also, as shown in the drawing, deflecting the strip out of a straight pass line for the same reason above stated in relation to the roller 12. The lower portion of the roller 14a is immersed in masking substance 15, preferably an alkali metal borate in water solution. As indicated above, sodium tetraborate will normally be used because of its ready availability and relatively low cost. The advantages of using an alkali metal borate as a masking substance have been explained above.

After application of the masking substance the strip passes over a heating unit 16 which dries the masking substance. Both in the case of the flux and in the case of the masking substance the coating is applied in water solution and the heating unit following the coating applying roller evaporates the water, leaving a substantially dry coating of flux or masking substance as the case may be upon the strip. As the strip passes to the guide roll 5 its upper surface is covered with a dry coating of flux and its lower surface is covered with a dry coating of masking substance.

The strip passes about the guide roll 5, upwardly through a heater 17, about guide rolls 6 and 7 and downwardly through a heater 18. The heaters 17 and 18 raise the temperature of the strip to a temperature approaching that of the bath of molten spelter through which the strip is to be passed, but the strip is not heat treated at a temperature even approaching 1250 F. and the strip is not subjected to a reducing atmosphere when being heated by the heaters 17 and 18. The alkali metal borate has no deleterious effect on the strip and effectively covers one surface thereof.

The galvanizing pot is designated by reference numeral 19 and contains a bath 20 of molten spelter. The guide rolls 8 and 9 are journaled for rotation beneath the surface of the spelter in the galvanizing pot 19 and the strip, coated on one face with dry flux and on the opposite face with dry masking substance, passes through the bath of molten spelter about the guide rolls 8 and 9 and up out of the bath between the exit rolls 21. The fiuxed side of the strip, which is the upper side between the guide rolls 8 and 9, is effectively galvanized while the opposite side of the strip, i.e., the under side between the guide rolls 8 and 9, to which the masking substance was applied remains ungalvanized, the masking substance inhibiting adherence of spelter to the side of the strip bearing the masking substance.

As the strip emerges from the galvanizing bath through the exit rolls 21 the small amounts of oxides and metal which may lightly cling to the masking substance may be removed by suitable removing means acting on the ungalvanized side of the strip. The removing means are indicated in the drawing by a diagrammatic representation of a brush 22. As the arrow indicates, the brush may be rotated so that it turns counter to the direction of advance of the strip. The brush may be of various materials; we find that a brush of thin flexible wire serves adequately to remove the lightly adhering oxides and metal. The masking substance remains on the ungalvanized portion of the strip until the strip passes through the cooling zone 23 and then, after cooling, if it is desired to remove the masking substance prior to subsequent treatment, it may be easily removed by Water.

The strip passes about the guide roll 10 and through a cooling unit 23 whence it may pass to a roller leveler and either a shear for shearing the strip into sheets or a reel for forming the strip into a coil.

While we have shown the flux and masking substance being applied by rolls while the strip is moving generally horizontally, the flux and masking substance may be applied by rolls while the strip is moving generally vertically or at an acute angle to the horizontal and may be applied otherwise, as, for example, by spraying, while the strip is moving generally horizontally or generally vertically or at an acute angle to the horizontal.

While we have shown and described a present preferred method of practicing the invention it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously practiced within the scope of the following claims.

We claim:

1. A method of applying a protective metal coating to a a portion only of a ferrous metal article while maintaining the remainder thereof substantially free from oxide, obviating a high temperature oxide-removing heat treatment, comprising coating with a solution of an alkali metal borate the portion of the article which is not to be metal-coated and dipping the article in molten coating metal whereby to metal-coat the portion of the article which is not coated with the alkali metal borate while the portion coated with the alkali metal borate remains uncoated with the coating metal and substantially free from oxide and limiting the temperature of the article and the bath during such treatment to a temperature below the melting point of the alkali metal borate, thereby producing an article having a portion metal-coated and the remainder substantially free from oxide.

2. A method of galvanizing a portion only of a terrous metal article while maintaining the remainder thereof substantially free from oxide, obviating a high temperature oxide-removing heat treatment, comprising coating with a solution of an alkali metal borate the portion of the article which is not to be galvanized and dipping the article in molten spelter whereby to galvanize the portion of the article which is not coated with the alkali metal borate while the portion coated with alkali metal borate remains ungalvanized and substantially free from oxide and limiting the temperature to which the article is subjected during such treatment to the temperature of the molten spelter, thereby producing an article having a portion galvanized and the remainder substantially free from oxide.

3. A method of galvanizing a portion only of a ferrous metal article while maintaining the remainder thereof substantially free from oxide, obviating a high temperature oxide-removing heat treatment, comprising coating with a flux the portion of the article which is to be galvanized and coating with a solution of an alkali metal borate the portion of the article which is not to be galvanized and dipping the article in molten spelter whereby to galvanize the portion of the article which is coated with flux while the portion coated with alkali metal borate remains ungalvanized and substantially free from oxide and limiting the temperature to which the article is subjected during such treatment to the temperature of the molten spelter, thereby producing an article having a portion galvanized and the remainder substantially free from oxide.

4. A method of galvanizing one side only of ferrous metal strip while maintaining the other side thereof substantially free from oxide, obviating a high temperature oxide-removing heat treatment, comprising coating one side of the strip with a solution of an alkali metal borate and passing the strip through a bath of molten spelter whereby to galvanize the side of the strip which is not coated with the alkali metal borate While the side coated with alkali metal borate remains ungalvanized and substantially free from oxide and limiting the temperature to which the strip is subjected during such treatment to the temperature of the molten spelter, thereby producing a strip having one side galvanized and the other side substantially free from oxide.

5. A method of galvanizing one side only of ferrous metal stri while maintaining the other side thereof substantially free from oxide, obviating a high temperature oxide-removing heat treatment, comprising coating one side of the strip with a flux and coating the other side of the strip with a solution of an alkali metal borate and passing the strip through a bath of molten spelter whereby to galvanize the side of the strip which is coated with flux while the side coated with alkali metal borate remains ungalvanized and substantially free from oxide and limiting the temperature to which the strip is subjected during such treatment to the temperature of the molten spelter, thereby producing a strip having one side galvanized and the other side substantially free from oxide.

References Cited by the Examiner UNITED STATES PATENTS 201,340 3/78 Ferguson 118-223 890,853 6/08 Fessler 113--126 1,567,632 12/25 Whinfrey 14822 1,742,214 1/30 Owston 118246 1,835,113 12/31 Iredell 11753 X 1,862,249 6/ 32 Wilder 117--51 1,928,714 10/33 Whitney 113127 2,343,158 2/44 Scott 29-490 2,498,485 2/50 Clawson 1175.5 2,557,983 6/51 Linder 1i175.5 2,559,969 7/51 Kennedy 117-5 .5 2,689,545 9/54 Nelson 118-246 2,709,516 5/55 Trembicki 117-169 2,894,850 7/ 59 Greene et a1. 117-5.5

RICHARD D. NEVIUS, Primary Examiner. JOSEPH B. SPENCER, Examiner. 

1. A METHOD OF APPLYING A PROTECTIVE METAL COATING TO A PORTION ONLY OF A FERROUS METAL ARTICLE WHILE MAINTAINING THE REMAINDER THEREOF SUBSTANTIALLY FREE FROM OXIDE, OBVIATING A HIGH TEMPERATURE OXIDE-REMOVING HEAT TREATMENT, COMPRISING COATING WITH A SOLUTION OF AN ALKALI METAL BORATE THE PORTION OF THE ARTICLE WHICH IS NOT TO BE METAL-COATED AND DIPPING THE ARTICLE IN MOLTEN COATING METAL WHEREBY TO METAL-COAT THE PORTION OF THE ARTICLE WHICH IS NOT COATED WITH THE ALKALI METAL BORATE WHILE THE PORTION COATED WITH THE ALKALI METAL BORATE REMAINS UNCOATED WITH THE COATING METAL AND SUBSTANTIALLY FREE FROM OXIDE AND LIMITING THE TMEPERATURE OR THE ARTICLE AND THE BATH DURING SUCH TREATMENT TO A TEMPERATURE 